A GOP strategist has a dire warning for Republicans about winning future presidential elections

Donald Trump. AP Photo/Gerald Herbert A fiercely anti-Donald Trump GOP strategist explained in a new book how the Republican Party can gain millennial and urban support and capture a future presidency after a tumultuous 2016 election cycle concludes.

Siegfried pointed to states such as North Carolina, Virginia, Colorado, Nevada, Iowa, and New Mexico — all of which have leaned toward Democratic nominee Hillary Clinton in recent polling — as states that Democrats have pushed from "red" to "purple" over the past two decades. He said that this was a result of Republicans not challenging them in strongholds like California, New York, and Illinois.

"Because the Republicans were no longer challenging Democrats in urban areas, the Democrats didn't have to spend money and resources defending their home turf," he wrote in the book. "Instead, they took these savings and decided to put the GOP on the defensive in areas where it was previously strong."

He said that that push began in the 1990s and first proved majorly successful in 2008, when President Barack Obama captured many states once associated with the GOP and held on to most of them in his 2012 reelection effort.

"These are all states that the Democratic Party targeted, established a beachhead in, and then slowly built up a presence that moved the electorate," he wrote. "What states has the Republican Party done this same thing to? None."

He put forth three points on what would happen if the GOP went through with his plan:

By challenging Democrats in Democratic strongholds, Democrats would be forced to spend resources that would've been dedicated to swing states.

Republicans would make progress with voting blocks such as inner-city African-Americans and Hispanics. While he said that "a majority" would not cross over, some would move away. That would also "help to kill charges that the GOP doesn't care about minority voters."

Over a prolonged period, the targeted states could move into swing-state territory, which would further thin Democratic resources.

The policy platform for such an initiative, he said, is to come down on the side of supporting same-sex marriage, buying into climate science and combating climate change, and using "conservative ideas" in dealing with social-justice issues while maintaining traditional conservative ideals on education, gun rights, the economy, and foreign policy.

"This book was written because Republicans have a path to winning in the future, but it is a path that some are reluctant to take or simply just don't know how to begin the journey," he wrote.